Flow of water through carbon nanotubes predicted by different atomistic water models

Nonequilibrium molecular dynamics simulations are reported to investigate the influence of different atomistic water models on the predicted flow behavior in carbon nanotubes (CNTs) with diameters between 0.81 nm and 1.9 nm. The comparison was made using rigid three-site [simplified point charge (SPC), extended SPC (SCP/E), and transferable intermolecular potential three point (TIP3P)] and four-site (TIP4P and TIP4P/2005) models. In addition, a flexible three-site model (SPC/Fw) was also investigated. The effect of different simulation conditions was determined by generating a flux across the CNT using either a pressure gradient across a membrane separating two water reservoirs or a periodic CNT with a constant force applied to each water molecule. Simulations involving the two water reservoirs indicate that the flux is strongly dependent on the choice of water model, which confirms earlier work. By contrast, this strong model dependency is not a feature of the periodic CNT simulations. Instead, the flux depends mainly on the pore diameter and the molecular density of water inside the CNT. The influence of the water model becomes very small in the periodic CNT simulations, which eliminates distorting entrance/exit effects.